Fuse



P 1950 J. B. OWENS 2,523,139

FUSE

Filed Sept. 28. 1946 fnerf Granu/ar g4 fnsu/of/ny Mafer/a/ WITNESSES:INVENTOR 4 kmesfi. Owens.

Patenteci Sept. 19, 1950 FUSE James B. Owens, Pittsburgh, Pa., assignorto Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application September 28, 1946, Serial No.700,072

9 Claims.

This invention relates to electric circuit interrupters, and morespecifically to such interrupters of the fusible type which are adaptedto limit the current during circuit interruption.

Electrical apparatus of low current rating when connected to highcurrent circuits is likely to explode or suffer considerable damage inthe event of an internal fault. In order to adequately protect suchapparatus, it is necessary that the circuit to a faulty device be openedvery quickly and the fault current limited. Attempts have been made togroup several low current devices such as capacitors in a bank andprotect the bank with current-limiting power fuses. These attempts havefailed however, since such fuses are unable to limit the current to alow enough value to prevent explosion of a faulty unit before thecircuit is opened.

Accordingly, one object of this invention is to provide a novel currentlimiting fuse adapted for the individual protection of low currentapparatus, such as capacitor units or the like.

Another object of this invention is to provide a novel current limitingfuse especially adapted for mounting on and protection of individualcapacitor units.

A further object of this invention is to provide a current limiting fusehaving novel means providing for visual indication of operation of thefuse to interrupt the circuit.

A more specific object of this invention is to provide in a currentlimiting fuse having fusible strain means for normally retainingindicating means at a nonindicating position, means providing currentlimiting action upon fusion of such 7 strain means as well as uponfusion of the main current-carrying fusible means.

A more general object of this invention is to provide a novel currentlimiting fuse which is small in size and economical to manufacture andis especially constructed for mounting on an individual capacitor unit,and yet is capable of limiting fault currents to a low enough value andof interrupting the circuit soon enough to prevent the building up ofdangerous pressures due to internal faults in such unit.

These and other objects of this invention will become more apparent uponconsideration of the following detailed description of a preferredembodiment thereof, when taken in connection with the attached drawing,in which:

Figure 1 is a longitudinal section View taken through a fuse embodyingthis invention with certain of the interior parts shown in elevation;and

iii

Fig. 2 is a transverse section view taken substantially on the line II-II of Fig. l.

The embodiment of the invention shown on the drawing comprises a fusehaving a tubular holder 2 of insulating material, such as fiber or asynthetic resin. The lower end of the holder 2 is adapted to be closedby a terminal closure plug 4 which is threaded into the lower end of theholder, and secured as by a pin 6. Terminal plug 4 is provided with asubstantially centrally located tapped opening 8, which is adapted to bethreaded onto the terminal of a capacitor unit, so that the fuse may bemounted directly on the unit and be directly supported therefrom. Thetapped opening 8 in closure plug 4 merges at its inner end into apassage H! of less crosssection area than opening 8, and this passageextends inwardly to be formed in part in a sleeve extension I2 of theclosure plug.

A rod 14 of insulating material is adapted to be supported within fuseholder 2, being secured in position by a screw I5 extending throughpassage [0 of closure plug 4 to be threadedly engaged in a tappedopening in the lower end of rod [4. Preferably, rod I4 is of aninsulating material which is capable of evolving an arcextinguishing gaswhen in proximity to an electric arc, such, for example, as fiber or thelike, all for a purpose to be described. Rod I4 is provided with a pairof spiral slots I8 and 20 on the surface thereof, with one slot 18adapted to receive a fuse wire 24 therein, and the other slot 20 adaptedto receive a strain wire 22. Fuse wire 24 is of a low resistanceconducting material, such, for example, as silver, Whereas strain wire22 is of a relatively higher resistance material, such as acopper-nickel alloy. Slots l8 and 20 are spaced apart and extend ingenerally parallel relation along the length of rod I4 terminating atthe opposite ends of the rod. The lower end of fuse wire 24 and strainwire 22 are secured as by soldering or the like. to sleeve l2 onterminal plug 4, so as to be electrically connected therewith.

A closure disc 26 is provided in holder 2 at the upper end of rod M forenclosing the space between the upper end of the rod and terminal plug4. Closure disc 26 is preferably of an insulating material, such asfiber, and is held in position by a terminal collar 28, which in turn issecured in the fuse holder by a terminal screw 30 extending through anopening 3| in the side of holder 2 and having its inner end threadedinto a tapped opening in terminal collar 28. Preferably, terminal screw30 is secured against rotation in collar 28 as by a pin 29, and has apair of nuts 32 on the outer end thereof for securing a line conductorthereto.

Mounted in holder 2 above terminal collar 28 is an inverted generallycup-shaped indicator 34 having an outwardl extending flange 3? at theinner end thereof, which is adapted to engage a stop disc 38 to limitoutward movement of the indicator. Stop disc 38 may be held in positionby any desired means, such, for example, as by the split retainin ring42, which is received in a groove provided adjacent the upper end of theholder 2. A coil compression spring 32 reacts between terminal collar 28and flange 3'! of the indicator to bias the indicator outwardly relativeto holder 2, but strain wire 22 extends upwardly through an opening inclosure disc 26 to have its upper end extend through a central opening45 in the indicator and be secured thereto as by soldering 44, or thelike.

The upper end of fuse wire 24 extends through another opening in closuredisc 26 and is secured to terminal collar 28 in any desired manner, forexample, as by soldering or the like. It is now apparent that fuse wire24 is in series in the circuit through the device shown, being connectedto terminal collar 23 and terminal screw 3t at its upper end and beingconnected to terminal plug 4 at its lower end.

The particular structure described above, wherein strain wire 22 andfuse wire 24 are located in slots l8 and 20, is especially designed sothat when these wires are melted, the resulting arc will be so confinedand acted upon as to create a high enough arc voltage that the :1.

current flow at that time will be limited to a value less than theparticular fault is capable of causing, and in order to interrupt thecircuit before any appreciable damage to the protected capacitor isaccomplished this structure also is especially arranged to interrupt thecircuit at the first current zero. It is essential that the current belimited in a small fraction of a half cycle in order to prevent seriousdamage, and for this purpose it will be noted that the slots i and 26are made to be of substantially the same size as fuse wire 24. Since anare formed within these slots would tend to blow out of the slots, aplurality of spaced washers 46 are provided along the length of rod M toretain correspondingly spaced portions of the arc within the slots. Thewashers 46 are of an insulating material, such as fiber or the like.When an arc is struck in slot l3 or 2D, the arc voltage will immediatelyrise at a rapid rate due to restriction of the arc cross section in thenarrow confines of the arc passage, and it will be extinguished at thefirst current zero by the arcextinguishing action of the slot itself.The gases evolved from the material comprising the slot walls will bedirected by the slot transversely through the arc and will then ass intothe finely divided inert insulating material 48 occupying the spacebetween rod 14 and the inner walls of holder 2. This transverse blast ofgas effectively de-ionizes the arc path because it acts to sweep allmetal vapor and other ionized particles in the arc path into thematerial 43 where it is dispersed and/or condensed in separatedinsulated relation. As stated above, the width of slots i8 and is madeas small as possible being limited only by the diameter of fuse wire 2%,and the depth of the slots is preferably greater than the slot width,being on the order of about twice the slot width.

While the lower end of strain wire 22 is connected to terminal plug 4,the upper end thereof being connected to indicator 2% which in turn iselectrically connected with terminal collar 28 by the turns of coilspring 42, means that this element is connected in parallel with fusewire 24 between terminals 4 and 30. However, since strain wire 22 is ofa relatively high resistance material which may also have a greatermechanical strength than fuse wire 24, it is smaller in cross-sectionand normally carries only a very small current. Accordingly, when afault occurs, fuse wire 24 melts first, and the voltage appearing acrossstrain wire 22 causes a current to flow in it to fuse the strain wire.While the arc will usually persist in the slot occupied by fuse wire 24when strain wire 22 is melted, and be finally interrupted in slot [8, itis obvious that by providing strain wire 22 in a similar slot 22, if thearc should transfer to the path occupied by the strain wire, it will beextinguished, and the current will be limited in the same mannerdescribed above.

When strain wire 22 melts, indicator 34 is no longer held at the innerposition shown in Fig. l, and spring 42 is free to move it outwardlyrela tive to holder 2 until its flange 37 engages stop disc 38, at whichposition it will be readily visible to indicate blowing of the fuse.

It is apparent from the foregoing that the fuse structure describedabove provides for current limitation and fast interruption of thecircuit in a fuse especially designed for mounting on and the protectionof capacitor units and the like. Moreover, this fuse further includes ameans for givin a clear visible indication of the blowing of the fusewithout interfering in any way with the efficiency of the fuse to eitherlimit the current or rapidly interrupt the circuit. This last feature isvery important where capacitors are being protected, because they areusually grouped in banks containing a great many capacitor units, and itwill be appreciated that it is very difficult to determine which unitsare faulty unless a dependable fuse indication is incorporated in eachfuse.

Having described a preferred embodiment of this invention in accordancewith the patent statutes, it is desired that this invention be notlimited to this particular embodiment inasmuch as it will be apparent,particularly to persons skilled in this art, that many modifications andchanges may be made in this particular structure without departing fromthe broad spirit and scope of the invention. Accordingly, it is desiredthat the invention be interpreted as broadly as possible and that it belimited only as required by the prior art.

I claim as my invention:

1. In a. fuse, a tubular fuse holder of insulating material havingspaced terminals thereon, solid means of insulating material positionedin said holder and extending longitudinally thereof, a plurality ofcontinuous generally parallel narrow spiral passages formed as groovesin the outer surface of said solid means, a fuse wire in one of saidpassages connected between said terminals, a relatively high resistancestrain wire in another of said passages also connected between saidterminals, and indicating means movably mounted on said holder and beingbiased for movement relatively to the holder but normally beingrestrained by said strain means.

2. In a fuse, a tubular fuse holder of insulating material having spacedterminals thereon,

solid means of insulating material positioned in said holder spaced fromthe inner walls of said holder and extending longitudinally thereof, aplurality of continuous generally parallel nar row passages in the formof grooves in the outer surface of said solid means and extending alongthe length thereof, a fuse wire in one of said passages connectedbetween said terminals, a relatively high resistance strain wire inanother of said passages also connected between said terminals, andindicating means movably mounted on said holder and being biased formovement relatively to the holder but normally being restrained by saidstrain means.

3. In a fuse, a tubular fuse holder of insulating material, spacedterminal means on said holder one of which is adjacent to but spacedinwardly from one end thereof, indicating means movably mounted in saidone end of said holder outwardly of said one terminal means and biasedto move from a position wherein a major portion thereof is within saidholder to a position wherein a substantial portion thereof projects fromsaid one end of the holder, and fusible strain means in said holderconnected between said terminals and directly engaging said indicatinmeans for normally maintaining the latter at its inner position.

4, In a fuse, a tubular fuse holder of insulating material, spacedterminal means on said holder one of which is adjacent to but spacedinwardly from one end thereof and extends through the side wall of saidholder, indicating means movably mounted in said one end of said holderoutwardly of said one terminal and biased to move from a positionwherein a major portion thereof is within said holder to a positionwherein a substantial portion thereof projects from said one end of theholder, and fusible strain means in said holder connected between saidterminals and directly engaging said indicating means for normallymaintaining the latter at its inner position.

5. In a fuse, a tubular fuse holder of insulating material, spacedterminal means on said holder one of which is adjacent to but spacedinwardly from one end thereof and extends through the side wall of saidholder, indicating means movably mounted in said one end of said holderoutwardly of said one terminal and biased to move from a positionwherein a major portion thereof is within said holder to a positionwherein a substantial portion thereof projects from said one end of theholder, fusible means in said holder directly connected between saidterminals, relatively high resistance fusible strain means directlyconnecting the other of said terminals and said indicating means, andsaid indicating means being at least in part of an electrical conductingmaterial which is in conductive relation with-said one terminal.

6. In a fuse, a tubular holder of insulating material, a terminalclosure at one end of said holder, terminal means secured in said holderat a point adjacent to but spaced from the other end thereof and havinga terminal portion extending through a side opening in said holder tothe exterior thereof, closure means for said other end of said holderlocated within said holder adjacent said terminal means, indicatingmeans movably mounted in said other end of said holder outwardly of saidterminal means and biased to move from a position wherein a majorportion thereof is within said holder to a position wherein asubstantial portion thereof projects from said other end of the holder,fusible means and are controlling means in said holder between saidclosures, and said fusible means being connected between said terminalsand including a strain portion extending through said closure means fornormally holding said indicating means at its inner position. I

'7. In a fuse, a tubular holder of insulating material, a terminalclosure atoneend of said holder, terminal means secured in said holderat a point adjacent tobut spaced from the other end thereof and having aterminal portion extending through a side opening in said holder to theexterior thereof, closure means for said other end of said holderlocated within said holder adjacent said terminal means, indicatingmeans movably mounted in said other end of said holder outwardly of saidterminal means and biased to move from a position wherein a majorportion thereof is within said holder to a position wherein asubstantial portion thereof projects from said other end of the holder,fusible means and are controlling means in said holder between saidclosures, said fusible means comprising a low resistance fusible elementand a relatively high resistance fusible strain element supported inspaced insulated relation in said holder and being connected in parallelcircuit relation between said terminals, and said strain elementextending through said closure means for normally holding saidindicating means at its inner position.

8. In a fuse, a tubular fuse holder of insulating material having spacedterminals thereon, solid means of insulating material positioned in saidholder spaced from the inner walls of said holder and extendinglongitudinally thereof, a plurality of generally parallel narrowpassages in the form of continuous grooves in the outer surface of saidsolid means and extending along the length thereof, at least inner wallsof said passages being of a material capable of evolving anarcextinguishing gas when in proximity to an electric arc, means of aninert finely divided insulating material in the space between said solidmeans and holder, a fuse wire in one of said passages connected betweensaid terminals, a relatively high resistance strain wire in another ofsaid passages also connected between said terminals, and indicatingmeans movably mounted on said holder and being biased for movementrelatively to the holder but normally being restrained by said strainmeans.

9. In a fuse, a tubular fuse holder of insulating material having spacedterminals thereon, solid means of insulating material positioned in saidholder spaced from the inner walls of said holder and extendinglongitudinally thereof, a plurality of generally parallel narrowpassages in the form of continuous grooves in the outer surface of saidsolid means and extending along the length thereof, at least inner wallsof said passages being of a material capable of evolving anarcextinguishing gas when in proximity to an electric arc, means of aninert finely divided insulating material in the space between said solidmeans and holder, spaced barriers alon the open sides of said passagesbut covering only a minor portion thereof for preventing the escape ofcorrespondingly spaced portions of an arc therefrom, a fuse wire in oneof said passages connected between said terminals, a relatively highresistance strain wire in another of said passages also connectedbetween said terminals, and indicating means movably mounted on saidholder and being biased for movement relatively to the holder butnormally being restrained by said strain means.

JAMES B. OWENS.

REFERENCES CITED The following references are of record in the file ofthis patent:

Number 8 UNITED STATES PATENTS Name Date Slepian et a1 Sept. 26, 1933Slepian et a1. Nov. 28, 1933 Rawlins et a1. Feb. 9, 1937 Smith, Jr. Jan.10, 1939 Thommen et a1. Jan. 28, 1941 Rawlins et a1. Jan. 19, 1943

